1. Field of the Invention
The invention generally relates to a traveling wave tube (TWT). In particular, the invention relates to sealing of a vacuum envelope of a helix TWT.
2. Description of the Related Art
A traveling wave tube (TWT), also known as a traveling wave tube amplifier (TWTA), is a vacuum electron device used for amplification of relatively high power and relatively high frequency radio frequency (RF) signals. One type of TWT uses a helix as a slow-wave structure for the RF signals.
As a vacuum electron device, an interior of a TWT is maintained at a vacuum. Electrical connections between the interior and the exterior of the device are hermetically sealed to maintain the vacuum. Conventional sealing techniques for electrically coupling to a helix of the TWT suffer from relatively many disadvantages. For example, conventional sealing techniques pass an electrical conductor through a hermetically-sealed window. These windows are fabricated from a relatively thin section of ceramic material, such as aluminum oxide (AlO) or beryllium oxide (BeO).
For relatively good RF performance, the hermetically-sealed window should be relatively thin. Making the window thin reduces the amount of insertion loss of the window due to dielectric effects, such as relatively high dielectric constants or relative permittivities and relatively high dissipation factors.
Disadvantageously, the thinness of the hermetically-sealed window compromises the structural integrity of the window. As a result, the windows are relatively easily cracked or broken due to mechanical stresses, such as the stress from insertion of a cable or other transmission line, vibration, and the like. The cracking or breaking of the window can render a TWT inoperative due to the loss of the internal vacuum environment.